The invention relates to marine propulsion devices, and, more particularly, to means for controlling the spark timing in marine propulsion device internal combustion engines.
In marine propulsion device internal combustion engines, the timing plate is typically mounted for rotation about the crankshaft axis to control the spark timing of the engine. In many cases, rotation of the timing plate also controls the throttle by way of a throttle cam which is mounted on the timing plate and a throttle cam roller which engages the throttle cam and which moves the throttle plate in response to movement of the throttle cam. Such an arrangement is disclosed in U.S. Soder Pat. No. 2,906,251, issued Sept. 29, 1959.
The throttle plate is normally biased toward the closed position, and the force biasing the throttle plate toward the closed position acts through the throttle cam roller and the throttle cam to exert on the timing plate a torque biasing the timing plate in the direction closing the throttle plate. Failure to counter this torque may allow the throttle plate to close during engine operation.
It is known to counter this torque either with a detent mechanism or by creating excessive frictional drag that will hold the timing plate in place. Both of these systems resist movement of the timing plate in both directions, although the torque only acts in one direction. Known detent mechanisms must be overcome by the operator in order to move the control handle. These mechanisms also have a rough feel, and they only permit the operator to set the throttle in discrete positions. Known frictional drag systems permit the operator to set the throttle at any position within a continuous range of positions, but the operator must overcome the frictional drag in order to alter the throttle setting.
Attention is directed to the following U.S. patents:
______________________________________ Favary 1,146,317 July 13, 1915 Cuff 1,211,550 Jan. 9, 1917 Greene, et al. 1,529,248 March 10, 1925 Mallory 1,886,566 Nov. 8, 1932 Pollari 2,858,819 Nov. 4, 1958 Elingsen 3,769,949 Nov. 6, 1973 Frahm 4,071,002 Jan. 31, 1978 ______________________________________